Along with improvements in performance and quality of liquid crystal displays, various demands have been made for polarizing plate protective films employed in polarizing plates.
Commonly employed as the polarizing plate protective film of liquid crystal displays is film which employs cellulose ester as a material. In view of assuring flatness, cellulose ester film is commonly produced employing a solution film-casting method, whereby the refractive index in the thickness direction of the film tends to be lower than that in the in-plane direction.
In Patent Document 1, described is a cellulose ester film which results in minimal degradation of the polarizer under high temperature and high humidity, and reduced optical anisotropy due to the incorporation of ethylenic polymers. However, when only ethylenic polymers are incorporated, rupture of the film tends to occur during the production process of the polarizing plates. Further, it is desirous to reduce the variation of retardation values. Specifically, it was found that in the horizontal electric field switching mode type or the in-plane switching mode (hereinafter referred to as an IPS type) liquid crystal display, when the image area luminance is adjusted based on the ambient brightness during viewing, visibility such as contrast or color shift varied.    Patent Document 1 Japanese Patent Publication for Public Inspection (hereinafter referred to as JP-A) No. 2003-12859